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3.
MESSAGE THEORY OF OPERATION
The controller uses a large area of memory, called the Message Buffer, to temporarily store the
messages that it is asked to send. The Message Buffer is a "FIFO" buffer (First-In, First-Out), which
means that the first message to arrive is the first one sent out. The purpose of the buffer is to
prevent overruns when several software programs need to send messages simultaneously.
The various messages are loaded into the buffer by the programs that need to send their
messages; the messages are unloaded by a program called the Message Handler. The Message
Handler needs to know the type of message it is unloading, so that it can operate the proper
hardware (DTMF encoder, tone encoder, etc.). The way we tell the Message Handler the type of
message we desire is with special Control Characters.
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